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Electron Doom Project.
http://www.retrosoftware.co.uk/forum/viewtopic.php?f=73&t=454		 Page 1 of 1
Author:  alexi [ Wed Mar 03, 2010 11:35 pm ]
Post subject:  Electron Doom Project.
Hi, don't get your hopes up yet as I've only just started the code for this and there's
not much to see. I've started this thread as I think I'll have quite a few questions as I work through this and hopefully have something to show by the end of it.

My fist question is about this:

http://codebase64.net/doku.php?id=base: ... iplication

I'm using it for signed multiply of 16bit * 16bit = 32 bit

It seems to all work fine but in the code for generating table 1 there's this:

.db $c9

which I assume is EQUIB &C9 in electron assembler, am I right? and what does it do?
Author:  PaulDv [ Thu Mar 04, 2010 12:18 am ]
Post subject:  Re: Electron Doom Project.
Hi. This sounds like an ambitious project! Will be interesting to see how it progresses.

alexi wrote:
.db $c9
which I assume is EQUIB &C9 in electron assembler, am I right? and what does it do?

Yep, that should be an EQUB instruction on the Electron. It's basically an optimisation to reduce the byte count of the code. C9 is the opcode for an immediate CMP instruction. The first time through the loop, the TYA following it is consumed as the operand of the CMP and as a side effect, the carry is cleared. Subsequent iterations branch back to the TYA instruction with the carry already in the required state.
Author:  alexi [ Thu Mar 04, 2010 1:10 am ]
Post subject:  Re: Electron Doom Project.
Quote:
Hi. This sounds like an ambitious project! Will be interesting to see how it progresses.


:D Don't expect anything too great and thanks for the info.
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